Microwell plates are used for various microbiological, molecular biological, cellular biological, and immunological procedures. Due to the high number of samples in each microwell plate, the Society of Biomolecular screening and the American National Standards Institute (ANSI) have published standards ANSI/SBS 1-2004 through 4-2004 for microwell plates concerning the particular dimensions and positions of wells or microwells, herein also referred to as vessels, for microwell plates having 96, 984, and 1536 wells. Microwell plates are used in particular for culturing of microorganisms or cells or for the Polymerase Chain Reaction (PCR).
PCR is a process used to amplify and copy a piece of DNA sequence across multiple orders of magnitude and is a vital technique in the field of molecular biology. In the PCR process, the DNA fragment is mixed in aqueous solution with complementary DNA primers and DNA polymerase enzyme and the mixture is taken through several thermal cycling steps. This thermal cycling process separates the double-helix of the target DNA sequence and initiates new DNA synthesis through the DNA polymerase catalyst. A typical thermal profile for the PCR reaction is shown below in Table 1, where ° C. is degrees Celsius.
TABLE 1StepTime DurationTemperature (° C.)Initial Denaturation2minutes94-95Denaturation20-30seconds94-95Primer Extension1minute72Final Extension5-15minutes72
The PCR reactions are typically carried out in microwells in arrays from 8 to 96 wells and volumes of 0.2-0.5 milliliters (mL).
Efficient heat transfer through the walls of the microwell to the reaction solution is required for strict temperature control during the PCR reaction process. In order to achieve efficient heat transfer, the PCR trays are designed with very thin microwell wall thicknesses, such as around 0.2 mm. Injection molding of these thin-wall trays becomes a significant challenge since an extremely high flow material is required to fill the thin microwell walls. In addition, the material needs to have sufficient heat resistance to avoid deformation during the PCR thermal cycling step, and optical clarity is desired so the liquid volume level can be observed. Typically, a polypropylene such as PD702 from LYONDELL BASELL is used for injection molding of the PCR trays. However, polypropylene is subject to softening at elevated temperatures such as those used in PCR denaturation cycles, which can cause PCR or other microfluidic components to become excessively flexible during processing, and/or be subject to warping or other physical deformation, and/or leaking.
Furthermore, single-component microwell plates comprising polypropylene are not particularly suited for being handled by automatic devices because their softness makes it difficult for automatic devices to grip them and their low dimensional stability can have the consequence that the proportioning needles will contact the walls while being introduced into the vessels. Two-component microwell plates comprising a unitary plate comprised of a two separate components including a skirt and frame portion made of a first material and having a plurality of holes in the frame portion, and an overmolded well and deck portion having a plurality of wells that protrude through the holes of the skirt and frame portion, but the second material must still meet the above-described challenges.